1. Field of the Invention
The present invention relates to a device for measuring the time of modification of the physical state of a fluid medium and, in particular, measuring the coagulation time of blood, of the kind comprising a vertical cup which contains the fluid such as plasma and the necessary reagents and in which a ferromagnetic ball is placed and is rotated by an external magnetic field.
2. Description of the Prior Art
Such a device is described more particularly in the European patent n.degree. 90 192 in which the ball thus driven moves freely on the flat and horizontal bottom of a cup. When the coagulation of the fluid which is contained in the cup takes place, which fluid is here blood plasma to which reagents have been added, the ball moves over a curve directed towards the inside because, so it seems, of the increase of mechanical resistance opposed by the contents of the cup, and its radial movement is detected by means well known in themselves.
The accuracy of measurements thus made leaves much room for improvement, since the radial movement of a ball towards the center of a cup of very small size is a physical magnitude which is difficult to detect and to evaluate satisfactorily. Furthermore, the reproducibility of such measurements is not good, because, particularly, of the complexity of the phenomena on which they are based.